The lake sink in Atlantic salmon smolt downstream migration

Area of Science:

• Ichthyology
• Ecology
• Conservation Biology

Background:

• Downstream migration of Atlantic salmon smolts through rivers is well-researched.
• Limited data exists on smolt survival in lake and reservoir environments.
• Still water environments may pose higher risks to migrating smolts compared to running waters.

Purpose of the Study:

• To estimate the survival rates and movement patterns of Atlantic salmon smolts during downstream migration through a river-lake system.
• To identify critical bottlenecks and quantify losses during lake passage.
• To assess the impact of lake migration on overall salmon population dynamics.

Main Methods:

• Radio tagging of wild and hatchery-reared Atlantic salmon smolts.
• Release of tagged smolts in the river upstream of the lake system.
• Tracking of individual smolts throughout their migration across two large lakes over two seasons.
• Calculation of mortality rates per kilometer and migration times.

Main Results:

• Over 90% of radio-tagged smolts perished during lake migration.
• Observed mortality rates ranged from 3% to 4% per kilometer of lake traversed.
• Significant individual variation in migration time through the lakes was recorded.
• Lake migration represented a major population sink, comparable to marine phase losses.

Conclusions:

• Downstream lake migration poses a substantial threat to Atlantic salmon populations, acting as a significant population sink.
• Factors such as travel distance, time, navigational complexity, and predation risk influence smolt survival in lakes.
• Salmon populations migrating through lakes are more vulnerable to environmental stressors, necessitating targeted management strategies.